This invention relates to the field of satellite collection of geophysical data, and more particularly to an improved method of processing ocean color data collected over a plurality of color channels by a satellite carried CZCS (Coastal Zone Color Scanner) so as to remove atmospheric contamination errors from the data.
One major promise of ocean color satellite data has been the possibility of quantitatively relating these data to bichemical ocean processes and ocean circulation.
A major problem with obtaining absolute ocean color measurements and imagery from a spaceborne sensor is caused by the intervening atmosphere. Ninety percent of the signal received by the satellite sensor is of atmospheric origin. Atmospheric removal algorithms have been developed that have had encouraging results. However, calculating the radiance attributed to aerosol scattering can have problems that are a result of incorrectly estimating the aerosol characteristics. It is desirable, therefore, to provide an improved method for eliminating atmospheric contamination in CZCS imagery by selecting the optimum aerosol characteristics that can be applied to the entire image.
It has been shown for continental air masses that aerosol optical thickness T.sub.A and single scattering albedo .omega..sub.A can be assumed to be a continuous function strongly dependent on wavelength and that the ratio of the aerosol optical thickness at specific wavelengths is related to a power law. Thus the approximation, ##EQU1## where .eta. is termed the Angstrom exponent
.omega..sub.A =single scattering albedo of aerosols PA1 .UPSILON..sub.A =aerosol optical thickness PA1 .THETA.=zenith angle from satellite PA1 .THETA..sub.o =solar zenith angle PA1 .lambda..sub.o =reference wavelength PA1 .lambda.=wavelength of interest PA1 .rho.=(.THETA.,.THETA..sub.o,.lambda.) scattering phase function
Atmospheric transmittance .tau. as a function of wavelength .lambda. may then be expressed as EQU .tau.(.lambda.)=(.lambda./.lambda..sub.o).sup..eta. [Eq. 2]